As well as omnidirectional antennae of the type described above, in principle completely different types of antenna are also known. Thus, U.S. Pat. No. 5,220,337 A for example discloses a directional radiator which is for example in the form of a cavity radiator having a plurality of slots, which are positioned offset in the circumferential direction on the circumferential side walls thereof, the slots being supplied separately via separate coaxial cables.
DE 10 2008 003 532 A1 discloses an antenna for satellite reception. This antenna comprises a broadband omnidirectional antenna having a monopole radiator, which is vertically polarised and rises above an earth plate or counterweight surface. In this context, the omnidirectional antenna is in the form of a dual-polarised antenna, the dual-polarised antenna comprising a horizontally polarised radiator in addition to the vertically polarised monopole radiator.
A broadband Vivaldi or Vivaldi-like antenna means is known in principle from the publication “Vu T. A. et al.: UWB Vivaldi Antenna for Impulse Radio Beamforming. In: NORCHIP 2009 conference report, pp. 1-5”. In this context, the shown and described Vivaldi antennae are formed with a microstrip structure.
Finally, U.S. Pat. No. 4,763,130 discloses an antenna arrangement comprising a cylindrical casing in which slots, which are positioned mutually offset in the circumferential direction and extend mutually parallel and parallel to the axial central axis, are formed in the radiator casing and are supplied by a supply means which extends in the interior of the radiator casing.
The object of the present invention is to provide an omnidirectional antenna which is in principle broadband, which offers a wider range of applications than the prior art and should also not take up much space.
The object is achieved according to the invention in accordance with the features specified in claim 1. Advantageous embodiments of the invention are specified in the dependent claims.
It may be considered very surprising that the antenna according to the invention provides further advantages—by comparison with conventional solutions—without the antenna as a whole taking up more space, for example.
By contrast with a generic single-polarised omnidirectional antenna, the antenna according to the invention instead consists of a dual-polarised omnidirectional radiator, and for this comprises a vertically polarised monopole radiator and an additional horizontally polarised radiator means.
The solution according to the invention can be achieved in that slots are formed in a conical or cylindrical radiator or radiator portion of a vertically polarised monopole radiator, and are positioned offset in the circumferential direction and extend in the axial longitudinal direction of the radiator. These make it possible to provide a corresponding supply means, via which the slots can be supplied so as to generate a horizontally polarised radiation pattern, within the generally rotationally symmetrical monopole radiator.
According to the invention, this can be provided by using corresponding coupling pins or coupling cables, which are preferably arranged internally in the hollow, rotationally symmetrical or at least approximately rotationally symmetrical monopole radiator in such a way that, coming from a supply point in the same circumferential direction, they cross the slots in the casing of the at least approximately rotationally symmetrical monopole radiator. The supply is preferably provided by a central star-shaped distribution point in the interior of the monopole radiator which is surrounded by a casing.
In this context, the supply structure can be formed in various ways. For example, a central supply point may be provided (on a circuit board), from which the supply lines for the slot radiators proceed. Equally, a tubular or frustum-shaped support (depending on the shape of the monopole radiator) could also be inserted into the interior of this radiator, on which the corresponding supply lines are formed using a galvanic contact with the electrically conductive casing of the monopole radiator. Various concepts can be implemented in this context. However, the supply can also be provided via coaxial cables or any other lines which consist of at least two conductors (two-wire line, microstrip, slot line etc.), the external conductor of each coaxial cable (one conductor) on one side of the slot and the internal conductor (the other conductor), which crosses the slot, on the other side of the slot being electrically galvanically (or capacitively) coupled.
The supply structure for the horizontally polarised radiator may also for example be provided via a microstrip line structure. In other words, a disc-shaped substrate (dielectric) is preferably arranged in the interior of the conical, frustum-shaped and/or cylindrical monopole radiator, specifically parallel to the counterweight surface, radial supply lines proceeding outwards from a central star-shaped distribution point and each subsequently proceeding in an arc shape in the same circumferential direction at a predetermined distance, which is as small as possible, from the casing of the cylindrical or frustum-shaped monopole radiator, to an endpoint, these arc-shaped line portions crossing and thus exciting the slots.
In a particularly preferred embodiment, however, a multiple Vivaldi antenna arrangement is provided as a horizontal radiator means as a supply structure for the slots in the casing of the monopole radiator.
As is known, a Vivaldi antenna is a special case of a longitudinal antenna, more specifically a special case of a tapered slot antenna (TSA), the edges or rims of the slots preferably widening in a funnel shape, with a defined exponential formula, from a closed end to the open end thereof. This slot which widens in a funnel shape thus acts as a radiator element, it being possible for the slot to be supplied and excited via a supply microstrip line which crosses the slot.
With corresponding selection of the geometric dimensions and appropriate dimensioning of the supply, Vivaldi antennae can me made very broadband.
In the context of the invention, Vivaldi antennae or other, in particular linearly tapered slot antennae have the advantage that they are easy to produce in terms of construction, they can be arranged inside the rotationally symmetrical hollow body of the monopole radiator (and thus do not contribute to an increase in the construction height), and above all the preferably exponential funnel shapes, that is to say the various radiation directions of the Vivaldi antennae, can be orientated directly with the slots in the rotationally symmetrical or approximately rotationally symmetrical construction of the casing of the monopole radiator. This construction and the construction between the Vivaldi antenna and the slot-shaped configuration in particular of the cylindrical casing of the monopole radiator result in a particularly broadband antenna without tolerance problems.
Various numbers of the aforementioned slots in the casing of the at least approximately rotationally symmetrical monopole radiator can be selected. The higher the number of slots, the more rotationally symmetrical the horizontal radiation pattern. Preferably, at least three or four slots extending in the circumferential direction of the casing of the monopole radiator are provided.
The length and width of the slots can be optimised in accordance with the frequency ranges used. The slots preferably end open in the vertical radiation direction of the monopole radiator, but may also be formed closed, in particular if they are dimensioned correspondingly longer. The slot structure can also be formed so as to repeat in the circumferential direction in such a way that it is formed in a U shape, that is to say consists of a double slot, it being possible in this case for the electrically conductive surface remaining between the slots to be held by a dielectric support construction, these constructions being inserted into the slots for filling for example. It would equally be possible to form the entire monopole radiator or large parts thereof on a dielectric body, on which the correspondingly electrically conductive casing is formed as a layer, again making it possible to form corresponding U-shaped double slots without difficulty by omitting electrically conductive layer portions.
The vertically polarised radiator means can be supplied via the central axis, that is to say the axis of symmetry, of the monopole radiator, for example by means of a series (capacitive) coupling for the monopole vertically polarised radiator, as is disclosed in DE 103 59 605 B4. In this case, the horizontally polarised radiator is preferably supplied by means of a coaxial cable, which first extends through a through-opening in the earth or counterweight surface and of which a particular cable length is arranged extending on the counterweight surface, until the coaxial cable is passed through a further through-opening in the casing of the monopole radiator, at which it is connected for example electrically conductively to this casing, into the interior thereof, specifically as far as an aforementioned star-shaped distribution point of a corresponding supply structure for exciting the slots.
The coaxial supply lines, which extend outside the generally rotationally symmetrical monopole radiator, for the horizontally polarised radiator means are preferably of a length which is selected in such a way that it is not a multiple of λ/2 for an operating wavelength which is used by the vertically polarised radiator.
However, in the context of the invention, the supply for the vertically and the horizontally polarised radiator may also be provided the other way round, in such a way that for example the supply for the horizontally polarised radiator is provided in the vertical central axis or axis of symmetry and the supply for the vertically polarised monopole radiator is provided outside this central axis or axis of symmetry.